Risk factors for severe Chlamydia pneumoniae pneumonia in children: a retrospective case–control study

Objective This study aimed to investigate the clinical characteristics of Chlamydia pneumoniae pneumonia (CPP) in children and analyze the risk factors for progression to severe pneumonia. Methods A total of 133 children with CPP were retrospectively enrolled from Hebei Children's Hospital between 2023 and 2025. Disease severity was classified according to the Guidelines for the Management of Community-Acquired Pneumonia in Children (2024 revision), and patients were divided into a non-severe group ( n = 99) and a severe group ( n = 34). Demographic characteristics, clinical manifestations, and laboratory findings were compared between groups. Multivariate binary logistic regression analysis was performed to identify independent factors associated with severe disease. Results Compared with the non-severe group, children in the severe group had a higher peak temperature and longer duration of fever (both P < 0.001). No significant differences were observed in the proportion of mixed infections or the distribution of pathogens between the two groups (all P > 0.05). Laboratory findings showed a lower lymphocyte percentage and higher levels of WBC, CRP, and IgA in the severe group (all P < 0.05). Multivariate analysis identified decreased lymphocyte percentage (OR = 0.943, 95% CI 0.895–0.994) and elevated IgA (OR = 2.227, 95% CI 1.284–3.972) as factors associated with severe CPP. Conclusion Decreased lymphocyte percentage and elevated serum IgA are associated with severe CPP in children, suggesting potential roles in risk stratification. Further multicenter prospective studies are warranted to validate and confirm these findings.